1. Field of the Invention
This invention relates to the mechanical structure of a personal computer, and more particularly, to providing several levels of access to media and components within a personal computer.
2. Background Information
Personal computer systems typically include electronic circuits mounted on a planar board, with various other circuits mounted on option, or feature, cards plugged into the planar board by means of connectors. This method allows the variation of features of the computer system by varying the option cards installed within the system. In some personal computer systems, the processor chip is also mounted on a card plugged into the planar board. In a desk-top type of system, the planar board is fastened in place to the system frame near the bottom of the system. The option cards extend upward from the planar board, being plugged directly into the planar board, or being plugged into an upward-extending riser card that is in turn plugged into the planar board. Various electromechanical devices within the system, such as diskette drives and hardfiles are typically also installed above the planar board.
A typical personal computer system also includes a number of other subassemblies installed above the planar board. Such devices may include the direct access storage devices (DASD devices) used to provide data and program storage in most personal computers. These devices include both devices with removable media, called floppy drives, and devices with fixed media, called hardfiles. A typical personal computer includes one or two such devices with removable media, each of which has a slot to which access must be available for the removal and replacement of magnetic media.
As a result of such configurations, desk-top personal computer systems must be almost completely disassembled before the planar board can be removed and replaced. This requirement causes particular difficulties because the planar board typically has the highest failure rate among system components. Particular problems are associated with the removal of option cards connected to peripheral devices, since the cables to such devices must be disconnected before the cards can be removed. Thus, much time is wasted in disassembly and reassembly of components in the event of a planar problem, which may occur during the process of building and testing the computer in a factory, or during the subsequent operation of the computer in the user's office. Furthermore, in the user's office the additional desk space, required for the placement of various components removed for access to the planar board, is often not available. What is needed is a means to provide for easy access to the planar board and to DASD components for service.
Personal computer systems are typically configured to accept a single type of planar board, with mounting holes in the planar board attached to a frame by means of screws, plastic snap fasteners, or a combination of screws and plastic snap fasteners. To reduce the emission of radio frequency interference by the system, the planar board is typically grounded through a number of paths. Conductive pads on the planar may be provided in annular spaces around mounting holes, being held against the frame by screws tightened through the holes. Conductive pads also may be provided in other locations, to be contacted by flexible spring members supported by the frame. Thus, the fixed locations of mounting features in the frame limit the system to accepting a single type of planar board. Since the characteristics of a computer system depend largely on the planar board, this limitation often means that a different frame is required for each different system.
Another problem with fixed locations for mounting the planar board arises from relatively small variations in the locations of mounting holes in the planar board and in the location of mounting features used for its attachment to the frame. Such variations, which are to be expected with any practical processes for manufacturing planar boards and system frames, sometimes make it difficult to install a planar board in a specific frame. Occasionally, such variations make it impossible to perform this installation, so that a planar board or a frame must be scrapped in the manufacturing process.
Thus, what is needed is a configurationally flexible means for mounting the planar board, including means for moving attachment points into various configurations, so that different kinds of planar boards may be accommodated. It is also desirable that the means for mounting be movable through small distances to accommodate variations in locations of features mounting a single kind of planar board.
A number of personal computers, such as the IBM Personal Computer, Model AT, are equipped with key-operated locks that can be locked to prevent the removal of the top cover, and therefore to prevent access to subassemblies within the computer system. Such locks may also function as electrical switches to prevent the unauthorized use of the computers. However, such locks tend to leave the system in either a totally locked or totally unlocked condition. For example, there is no condition in which the computer can be operated without hindrance while its internal subassemblies are protected from theft. What is needed is a flexible locking system, offering several levels of security through the use of a single lock, which may be placed in any of several positions through the use of a single key.